This invention relates to an improved process for preparing 2,5-dichloro-3-nitorbenzoic acid. This acid and processes for its preparation are well known to those of skill in the art. It is an important compound because of its herbicidal activity itself and because of its utility as an intermediate in the preparation of 2,5-dichloro-3-aminobenzoic acid, another important herbicidally active compound. The herbicidal activity of 2,5-dichloro-3-nitrobenzoic acid and its functional derivatives is described in U.S. Pat. No. 3,013,873, and the herbicidal activity of 2,5-dichloro-3-aminobenzoic acid, its functional derivatives and their preparation from the 3-nitro compounds are described in U.S. Nos. 3,014,063 and 3,174,842.
Heretofore, a widely used procedure for preparing 2,5-dichloro-3-nitrobenzoic acid involved the nitration of 2,5-dichlorobenzoic acid. While this procedure yields the desired 3-nitro compound it suffers from a number of inherent disadvantages. For example, this procedure results in the production of a significant amount of the corresponding 6-nitro compound as a by-product.
The separation of the unwanted 6-nitro isomer from the desired 3-nitro compound is extremely difficult and requires the use of elaborate and cumbersome purification procedures which result in low yields of the desired 3-nitro compound. Consequently, there exists a need for a more effective process for preparing 2,5-dichloro-3-nitrobenzoic acid in increased yields that avoids the need to resort to elaborate and cumbersome purification techniques.